1. Field of the Art
The invention relates to method and device for polishing the edge of a work, and more particularly relates to polishing the edge of a work by use of a rubber wheel (RBW=RUBBER BONDED WHEEL) containing abrasives, instead of using the slurry containing diamond particles for abrasives which may obstruct the tubes of the device and adversely affect the electromagnetic valves and further may be easily congealed at various places, wherein the heat produced by polishing operation is cooled down by air or water, thereby to maintain the quality of the polished work and further to significantly reduce the production cost as well as the running cost of the device.
2. Prior Art
The wafers such as silicon wafers are generally referred to the thin disk-shaped semiconductor elements, and are normally cut out from a refined cylindrical single crystal mother material. The wafer is polished on one side thereof just like a mirror surface and then the surface is provided with various semiconductor elements by way of etching. Further the wafer is required to have the peripheral edge thereof trimmed by way of the emery wheel of diamond and is then polished just like a mirror surface by way of the buff polishing wheel using the slurry, thereby to prevent the dusts from sticking to the surface of the peripheral edge.
Since the conventional polishing wheel is poor in the polishing ability by itself, the slurry containing diamond particles is used to polish the wafer utilizing the chemical etching effect of the slurry which is alkaline. The slurry is a gel which is a mixture of fine abrasive particles of diamond and an alkaline solution (about pH 11).
In case the slurry is used to polish a work, it is necessarily required to provide a solution having the silicon abrasive particles mixed into the slurry. The conventional polishing machine is provided with a separator which is used to separate the abrasive particles from the used slurry after this is recovered, so as to repeatedly use the slurry. The used slurry is, therefore, sent to the tank of the separator through the tubes and the electromagnetic valves. Such a slurry has a nature of hardening and sticking to the objects when it is retained in the tubes and the tank for a long period of time. This will obstruct the tubes and adversely affect the electromagnetic valves.
This is the reason that the slurry is often called as "a devil water". In order to avoid the obstruction of the tubes, it is required to design the series of tubes to have a flushing structure so as to enable the series of tubes to be washed away of the slurry immediately after the slurry has passed the tubes. Further the metal portions of the device including iron which contact the slurry is required to be the expensive stainless steel coated with Teflon having a thickness of about 0.1 mm so as to avoid the corrosion due to the slurry and also to prevent the slurry from sticking to the portions. Further the tubes must be the Teflon tubes which may be expensive 7 to 10 times as much as the ordinary vinyl tubes. Thus the conventional polishing machine is considerably expensive in the production cost as well as in the running cost.
Further, in case of polishing by use of the slurry, it is required to settle the slurry in the tank bath after the polishing operation to remove the slurry from the solution by washing by way of supersonic waves and then to proceed to the subsequent process. This will considerably reduce the operation efficiency in addition to the probability of adverse influence of the slurry etching upon the wafer. Therefore, it has long been desired to realize the method for polishing the work without using the slurry.
On the other hand, if a rubber wheel containing abrasives is employed instead of the buff wheel, the rubber wheel will be rapidly abraded because the rubber wheel can not yieldingly traverse with respect to the work. Further the rubber wheel will damage the work such as the wafer because the rubber wheel is not so soft as the buff wheel. It is, therefore, required to provide some compensation for the hard rubber wheel to suitably polish the work such as the wafer.